Polyethers which are employed as urethane materials are produced by various methods. As the methods, batch methods and continuous methods have been mainly known. The batch methods have such drawbacks as poor volume efficiency of the reaction vessel and long production time. On the other hand, in continuous production methods, the volume efficiency of the reaction vessel tends to be high, and the production time can be relatively shortened, and accordingly various methods have been conventionally proposed. For example, Patent Document 1 (East German Patent DD 203,735), Patent Document 2 (U.S. Pat. No. 5,689,012) and Patent Document 3 (JP-A-6-16806) propose a method for continuously producing a polyether by means of a double metal cyanide complex catalyst. Further, Patent Document 4 (JP-A-7-165907) proposes a method for continuously producing a polyether having a low degree of unsaturation.
Patent Document 1 proposes a method for continuously producing a polyether by means of a double metal cyanide complex catalyst by using a tubular reactor. However, a preliminary operation such as activation of the catalyst is essential, such being troublesome. Further, when a large scale reactor is employed so as to increase the production amount, mixing failure of the reaction liquid is likely to occur, and accordingly the polyether to be obtained tends to contain products having an extremely high molecular weight and have a high viscosity.
Patent Document 2 proposes a method for continuously producing a polyether having a narrow molecular weight distribution by means of a double metal cyanide complex catalyst, by circulating the reaction liquid and continuously charging materials and a catalyst, which is not activated, in the middle of the circulation. However, in this proposal, the pressure as a production condition is not described, and the molecular weight distribution depending upon presence or absence of the vapor phase is not mentioned.
Further, Patent Document 4 proposes a method to suppress the content of monools having an unsaturated bond (hereinafter referred to as unsaturated monool) in the product polyether by contriving combination of production equipment. However, an apparatus to remove unsaturated monools is provided, and thus the production equipment tends to be large scale as a whole.
On the other hand, Patent Document 3 proposes to bring out characteristics of the double metal cyanide complex catalyst by contriving the reaction apparatus. However, consideration of improved technique has been required because of demands for improvement in catalyst performance and precise production of polyethers (production while precisely controlling the molecular weight and the molecular weight distribution of polyethers) in recent years.
Under these circumstances, the present invention is to overcome these problems and to provide a production method capable of precisely producing a polyether, more particularly, it provides a production method for precisely producing a polyether having a relatively high molecular weight by means of a double metal cyanide complex catalyst.